One of the techniques for reconstructing damaged bone tissue, which has been in use for some time, comprises the use of bio-compatible materials able to facilitate growth of the tissue. These materials are mainly divided into two categories, Hydroxylapatites and Tricalcium-phosphates which represent the minerals which constitute human bones.
These materials are typically produced artificially and distributed in the form of highly-porous granules such as to facilitate, internally of the porosities thereof, formation of osteocytes, i.e. cells which constitute bone tissue.
As described in patent publications U.S. Pat. No. 4,769,011, U.S. Pat. No. 4,801,263 and U.S. Pat. No. 7,357,789, present methods comprise use of devices, substantially syringes, suitable for injecting these granules into cavities in which bone tissue is to be reconstructed.
These devices therefore comprise an injection chamber having a distal outlet mouth for the material and a proximal mouth, in which the granular material is inserted, and a plunger, which sealedly slides along the injection chamber, having an operating surface facing the distal mouth of the injection chamber, destined to push the material along the injection chamber.
As demonstrated also in U.S. Pat. No. 4,801,263, there exists a need to realise injection chambers having relatively very small geometric dimensions (i.e. having a diameter of the injection chamber of a few millimeters), such as to ensure a good handlability by the surgeon, while at the same time being capable of realising the exiting of the material from the distal mouth.
In effect, the porous and consequently rough nature of the material, together with the geometric irregularities of the granules, facilitate the formation of agglomerates which can constitute occlusions of the injection chamber and the distal mouth. Further, the substantially ceramic and therefore hard nature of the material constitute a highly abrasive agent against the walls of the chamber. This abrasive action adversely affects the flowability of the granulate itself.
The need for easy handling of the syringe and the requirement of operating on small-dimension fractures and lacerations induce designers to reduce the section of the injection chamber; on the other hand, the smaller the section of the injection chamber, the worse the flowability of the granulate; consequently the section of the injection chamber cannot fall below critical values without entailing a high risk of agglomeration and formation of blockages which in fact prevent the sliding of the plunger and therefore the exit of the granulate from the syringe.
The granular material currently used has a particle size of between 0.1 mm and 1.5 mm in diameter, while an optimal size of the syringes, such as to facilitate their handling, is 4.5 mm in diameter. This size represents a critical value since for higher values the risk of formation of occlusions is substantially zero while for values lower than the risk of compacting is very high. The formation of occlusions by the material remains one of the main unresolved drawbacks in the prior art.